Memory leak in custom-drawn widgetset in RenderWinControl()

• Lazarus/FPC Version: Lazarus 2.3.0 (rev main-2_3-1386-g23b2324f9f) FPC 3.2.3 x86_64-linux-gtk2
• Operating System: any
• CPU / Bitness: any

What happens

By lagprogramming from forum: https://forum.lazarus.freepascal.org/index.php/topic,62955.msg476376.html#msg476376 .

lcl/interfaces/customdrawn/customdrawnproc.pas has function RenderWinControl(var AImage: TLazIntfImage; var ACanvas: TLazCanvas; ACDWinControl: TCDWinControl; ACDForm: TCDForm): Boolean; A simple form with a TEdit on it run for a couple of seconds in Linux-customdrawn. The application ran with heaptrc unit, which made the console window print lots of memory leaks. One of them was related to line: lRegion := TLazRegionWithChilds.Create; The memory allocated for lRegion is never freed. As long as customdrawn is selected, the memory leak should be detectable on all operating systems.

This is the original code

function RenderWinControl(var AImage: TLazIntfImage; var ACanvas: TLazCanvas;
  ACDWinControl: TCDWinControl; ACDForm: TCDForm): Boolean;
var
  lWinControl, lParentControl: TWinControl;
  struct : TPaintStruct;
  lCanvas: TCanvas;
  lControlCanvas: TLazCanvas;
  lBaseWindowOrg: TPoint;
  lControlStateEx: TCDControlStateEx;
  lDrawControl: Boolean;
  lRegion:TLazRegionWithChilds;
begin
  Result := False;
 
  lWinControl := ACDWinControl.WinControl;
 
  {$ifdef VerboseCDWinControl}
  DebugLn(Format('[RenderWinControl] lWinControl=%x Name=%s:%s Left=%d'
    + ' Top=%d Width=%d Height=%d', [PtrInt(lWinControl), lWinControl.Name, lWinControl.ClassName,
    lWinControl.Left, lWinControl.Top, lWinControl.Width, lWinControl.Height]));
  {$endif}
 
  if lWinControl.Visible = False then Exit;
 
  // Disable the drawing itself, but keep the window org and region operations
  // or else clicking and other things are broken
  lDrawControl := ACDWinControl.IsControlBackgroundVisible();
 
  // Save the Canvas state
  ACanvas.SaveState;
  ACanvas.ResetCanvasState;
 
  // lBaseWindowOrg makes debugging easier
  // Iterate to find the appropriate BaseWindowOrg relative to the parent control
  lBaseWindowOrg := FindControlPositionRelativeToTheForm(lWinControl);
  ACanvas.BaseWindowOrg := Point(lBaseWindowOrg.X, lBaseWindowOrg.Y - ACDForm.ScrollY);
  ACanvas.WindowOrg := Point(0, 0);
 
  // Prepare the clippping relative to the form
  ACanvas.Clipping := True;
  ACDWinControl.Region.Rect := Bounds(lBaseWindowOrg.X, lBaseWindowOrg.Y - ACDForm.ScrollY,
    lWinControl.Width, lWinControl.Height);
  lRegion := TLazRegionWithChilds.Create;
  lRegion.Assign(ACDWinControl.Region);
  ACanvas.ClipRegion := lRegion;
 
  lControlCanvas := ACanvas;
 
  if (ACDWinControl.InvalidateCount > 0) and lDrawControl then
  begin
    ACDWinControl.UpdateImageAndCanvas();
    lControlCanvas := ACDWinControl.ControlCanvas;
    ACDWinControl.InvalidateCount := 0;
 
    // Special drawing for some native controls
    if (lWinControl is TCustomPanel) or (lWinControl is TTabSheet)
     or (lWinControl is TCustomPage) or (lWinControl is TNotebook)  then
    begin
      // Erase the background of TPanel controls, since it can draw it's own border, but fails to draw it's own background
      // and also erase the background for TTabSheet (children of TPageControl) and TCustomPage (children of TNotebook)
      lControlCanvas.SaveState;
      lControlCanvas.Brush.FPColor := TColorToFPColor(lWinControl.GetRGBColorResolvingParent());
      lControlCanvas.Pen.FPColor := lControlCanvas.Brush.FPColor;
      lControlCanvas.Rectangle(Bounds(0, 0, lWinControl.Width, lWinControl.Height));
      lControlCanvas.RestoreState(-1);
    end
    else if lWinControl is TCustomGroupBox then
    begin
      lControlCanvas.SaveState;
      lControlStateEx := TCDControlStateEx.Create;
      try
        lControlStateEx.Font := lWinControl.Font;
        lControlStateEx.Caption := lWinControl.Caption;
        lControlStateEx.ParentRGBColor := lWinControl.GetRGBColorResolvingParent();
        GetDefaultDrawer().DrawGroupBox(lControlCanvas, Point(0,0),
          Size(lWinControl.Width, lWinControl.Height), [], lControlStateEx);
      finally
        lControlStateEx.Free;
        lControlCanvas.RestoreState(-1);
      end;
    end;
 
    // Send the drawing message
    {$ifdef VerboseCDWinControl}
    DebugLn('[RenderWinControl] before LCLSendPaintMsg');
    {$endif}
    FillChar(struct, SizeOf(TPaintStruct), 0);
    struct.hdc := HDC(lControlCanvas);
    LCLSendEraseBackgroundMsg(lWinControl, struct.hdc);
    LCLSendPaintMsg(lWinControl, struct.hdc, @struct);
    {$ifdef VerboseCDWinControl}
    DebugLn('[RenderWinControl] after LCLSendPaintMsg');
    {$endif}
  end;
 
  // Here we actually blit the control to the form canvas
  if lDrawControl then
  ACanvas.CanvasCopyRect(ACDWinControl.ControlCanvas, 0, 0, 0, 0,
    lWinControl.Width, lWinControl.Height);
 
  // Now restore it
  ACanvas.RestoreState(-1);
 
  Result := True;
end;

The patch adds "lRegion.Free;" before the last "ACanvas.RestoreState(-1);"

diff --git a/lcl/interfaces/customdrawn/customdrawnproc.pas b/lcl/interfaces/customdrawn/customdrawnproc.pas
index 5170ddc72b..aeb36771b2 100644
--- a/lcl/interfaces/customdrawn/customdrawnproc.pas
+++ b/lcl/interfaces/customdrawn/customdrawnproc.pas
@@ -563,6 +563,8 @@ begin
   ACanvas.CanvasCopyRect(ACDWinControl.ControlCanvas, 0, 0, 0, 0,
     lWinControl.Width, lWinControl.Height);
 
+  lRegion.Free;
+
   // Now restore it
   ACanvas.RestoreState(-1);